Desmoid tumours are rare, locally aggressive soft tissue tumours that occupy an ambiguous space between benign and malignant disease. Biologically benign, lacking metastatic potential, desmoid tumours frequently recur despite treatment, and cause substantial morbidity through local invasion, organ involvement and associated chronic pain. This biological ambiguity is mirrored by wide variation in language with patients variously told their tumour is ‘benign’, ‘borderline’ or ‘cancer’. Drawing on patient experience, psycho-oncology literature and concepts from medical anthropology, this essay examines how diagnostic terminology in desmoid tumour care carries weight beyond mere semantics. It argues that desmoid tumours represent a paradigmatic ‘liminal diagnosis’, in which inconsistent clinical language has the capacity to compound psychological and social distress. By shaping treatment, relationships and well-being, language exerts a powerful influence that remains largely overlooked in research and clinical practice, highlighting the need for research investigating the direct impact of language on care and the patient experience.